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Peroxynitrite-mediated linoleic acid oxidation and tyrosine nitration were analysed in the presence of synthetic model neuromelanins: dopamine (DA) -melanin, cysteinyldopamine (CysDA) -melanin and various DA/CysDA copolymers. The presence of melanin significantly decreased the amount of 3-nitrotyrosine formed. This inhibitory effect depended on the type and concentration of melanin polymer. It was found that incorporation of CysDA-derived units into melanin attenuated its protective effect on tyrosine nitration induced by peroxynitrite. In the presence of bicarbonate, the melanins also inhibited 3-nitrotyrosine formation in a concentration dependent manner, although the extent of inhibition was lower than in the absence of bicarbonate. The tested melanins inhibited peroxynitrite-induced formation of linoleic acid hydroperoxides, both in the absence and in the presence of bicarbonate. In the presence of bicarbonate, among the oxidation products appeared 4-hydroxynonenal (HNE). CysDA-melanin inhibited the formation of HNE, while DA-melanin did not affect the aldehyde level. The results of the presented study suggest that neuromelanin can act as a natural scavenger of peroxynitrite.

The content of endogenous melanin in white Balb c and black C-57 Bl. mice affected Zn2+ and Co2+ accumulation, elimination and distribution following intraperitoneal administration of these ions. Elimination of Co2+ ions was significantly greater in white mice than in black mice. Accumulation of Zn2+ was higher than that of Co2+ and did not depend on melanin content in mice. The same response was observed upon administration of exogenous melanin. Both ions accumulated mainly in spleen and heart irrespective of melanin content.